1. Field of the Invention
This invention relates to methods and/or apparatus for purification of, or separation of, metal ore constituents from complex copper containing ores by use of sparged-gas flotation cells in various kinds of flotation processes.
2. Description of the Prior Art Re: Complex Copper-Containing Ores
Those skilled in this art will appreciate that no two ore deposits are alike and that processes for extracting economic minerals from deposits can be as different as the ore deposits because they vary in make-up of major and minor economic minerals, degree of dissemination, means of formation, degree of oxidation, grain size of minerals, mineral associations, quantities of minerals, porosity, permeability, and composition of gangue minerals.
Similarly, the processing of ore bodies also may vary with the treatment equipment used, the design of grinding circuit(s) and/or the reagents used to extract or separate various minerals. For example, several processes have been used to produce a rising flow of gas bubbles for froth flotation of certain minerals and/or metal constituents of a wide variety of ores. Moreover, within this overall process, the number of flotation tanks, size and type of such tanks, as well as the stages of separation, the reagents employed and the flow schemes are usually unique to a given type of ore deposit.
Separation of minerals by flotation may be divided into three major processes: (1) bulk flotation--the flotation of all economic minerals into a concentrate with the depression of gangue minerals and especially the case wherein the concentrate is floated in several stages to continuously remove the gangue before final treatment by leaching or smelting; (2) reverse or back flotation--the flotation of gangue minerals while the economic minerals are depressed and (3) differential flotation--the flotation of economic minerals while gangue minerals are depressed, and the case where a continued treatment results in the economic minerals being selectively separated by flotation of one or more economic minerals while depressing one or more other economic minerals. Moreover, in all of these flotation processes, and especially in the differential flotation processes, several stages of flotation are usually employed to obtain a final product. Differential flotation has been used successfully on several major complex ore types including copper porphyry, copper magmatic, lead-zinc ores, and copper lead-zinc ores. However, the object of differential flotation in the treatment of complex ores of the aforementioned types remains the economic advantage resulting from a separation of various major valuable economic minerals in such ores.
In copper porphyry ores, the major copper bearing economic minerals include chalcopyrite, covelite, chalcocite, bornite, enargite, digenite, native copper, cuperite, azurite, and malachite. Those skilled in this art will also appreciate that molybdenite is a major economic non-copper bearing mineral in copper porphyry ores. Moreover, those minor non-copper bearing economic minerals sometimes associated with a given copper porphyry ores may include electrum, tentrahedrite-tennantite, argentite, sphalerite, and galena (gold, silver, zinc, and lead bearing minerals). It should also be noted that pyrite and other iron sulfide bearing minerals in copper porphyry deposits usually are considered gangue materials. Those skilled in this art will also appreciate that "simple" copper ores (comprised of just one ore component and gangue, (e.g., one percent chalcopyrite or native copper and 99% gangue) can be treated in the same way as "complex" ores (those having several economic mineral components) can be treated by the process of this invention and that the terms "simple" and "complex" should be regarded as equivalent in the context of this particular invention.
In one widely practiced flotation process (see generally FIG. 7), copper porphyry ores are concentrated by a process which begins with the introduction of a slurry of such ores (in a ground and or milled state) into a first stage (often referred to as a "rougher flotation"), sparged-air-driven, froth flotation tank or system of such first stage tanks in order to produce a low grade copper-molybdenite concentrate. The concentrate from the first stage is then upgraded in a second stage (often referred to as a "rougher cleaner flotation"), sparged-air-driven, flotation tank or system of such second stage flotation tanks. It should also be noted that collector reagents may be added at different stages during the process; e.g., in the grinding mill producing the ore pulp just prior to its introduction into the flotation cells and in the flotation cells (as well as in multiple places in the overall process) to produce the desired results. For example, in the first and second stages of flotation, pyrite and other gangue minerals are typically "depressed" by the use of depressant agents such as cyanide and/or lime.
The concentrate from the second stage is then collected and transported to a third stage (differential flotation") tank or series of such tanks which also employ air-sparging in order to separate the copper constituents and other minor economic minerals from the molybdenite. In such a third stage, differential flotation, cell system, copper minerals are typically "depressed" through the use of sodium hydrosulfide, sodium sulfide, or ammonium sulfide. Moreover, burner oil is often used to "float" the molybdenite component of the ore. Other broad considerations regarding these reagents also may apply. By way of example, the collector reagents used during flotation processes are often controlled by the electrical nature of a given mineral's surface since the surface potential of every mineral is, to a large extent, unique. Thus, the ions that are chemiabsorbed on the surface of a given mineral establish a surface charge and are called potential-determining ions. Such potential determining ions may be composed of hydrogen or hydroxyl ions, collector ions, or ions that form complex ions with the ions on the mineral surface. Those skilled in this art also will appreciate that the activity of the potential determining ions at which the surface charge is zero, is called the point of zero charge (PZC). Chalcopyrite for example is known to have a PZC of from 2.0 to 3.0, while pyrite has a PZC of 6.2 to 6.9 and scheelite has a PZC of 10.2. The PZC is a major factor in determining the collector that must be added to the flotation circuit to be absorbed on the mineral which results in flotation. Thus, fatty acids are often employed as collector reagents for scheelite, but they generally will not work for pyrite and xanthate. Similarly, collector reagents used for pyrite will not work for scheelite and so forth.
Be that as it may, the tailings taken from the bottom of the differential flotation cell(s) of the third stage, which generally contain the majority of the copper bearing mineral component of the ore, are then usually pumped to a thickener. The resulting thickened product containing the copper concentrate produced by the overall flotation process, is thereafter sent (very often by slurrying and pumping transport pipes) to a smelter. This final copper concentrate also very often contains minor but still economically significant amounts of gold, silver, lead, and/or zinc minerals.
In copper magmatic deposits, the major copper bearing economic minerals typically include chalcopyrite, covelite, chalcocite, bornite, enargite, digenite, as well as native copper. Other major non-copper bearing economic minerals included in such ores might comprise: millerite, nickel bearing pyrrhotite, nickeline, pendlandite, cobaltite, glaucodot, and skutterudite (nickel and cobalt bearing minerals). Minor non-copper bearing economic minerals sometimes associated with copper magmatic deposits also may include electrum, tentrahedrite-tennantite, argentite, (gold, silver, bearing minerals). Zvyagintsevite, geversite, platinum tellurides, native platinum and palladium group minerals also are often found in varying economic quantities in copper magmatic deposits. Similarly, pyrite and other iron sulfide bearing minerals in copper magmatic deposits may or may not have economic minerals substituted into their crystal lattices.
Differential flotation processes (see generally FIGS. 8 and 9) are often applied to copper magmatic ores by a process which begins with the introduction of a slurry of such ores (in a ground and or milled state) into a first stage, sparged-air-driven, froth flotation tank or system of such tanks in order to produce a low grade copper-nickel concentrate or a copper-cobalt concentrate. The concentrate from the first stage is then upgraded in a second stage which also employs sparged-air-driven flotation tank or system of such flotation tanks. As in the case of the copper porphory ores, the collector reagents used in recovering copper magmatic ores may be introduced at different stages during the overall process, e.g., in the grinding mill, to the ore pulp just prior to its introduction into the flotation cells, to the flotation cells or at multiple points in the overall process. In the first and second stag flotations, pyrite and other gangue minerals are typically "depressed" by through the use of cyanide and/or lime. The concentrate from the second stage is then collected and transported to a differential flotation tank or series of such tanks which constitute a third stage of the overall process. These differential flotation tanks also employ air sparging in order to separate copper constituents and other minor economic minerals from cobalt or nickel constituents. In such a third stage, differential flotation cell system, copper minerals are typically separated from cobalt or nickel minerals through the simultaneous use of selective collector reagents and selective depression agents such as sodium cyanide.
The tailings taken from the bottom of such a differential flotation cell, which generally contain the majority of the cobalt or nickel bearing mineral component to the ore, are then conditioned with sulfuric acid, copper sulfate, and isopropyl xanthate in order to further "clean" these components. A resulting thickened product, containing the cobalt or nickel concentrate produced by the overall flotation process, is then sent (very often by slurry and pumping transport pipes) to a smelter. The final copper concentrate is also transported to a smelter. Here again, the greater part of minor economic platinum palladium, gold and silver minerals also reside in the copper concentrate.
In lead-zinc and lead-zinc-copper deposits, major economic minerals include galena, cerussite, anglesite, plumbojarosite, sphalerite, marmatite, (lead and zinc bearing minerals). Minor economic minerals sometimes include tentrahedrite-tennantite, argentite, sulphosalts of silver, ruby silver (silver bearing minerals), free gold, bismuth, and cadimum. The distinction between lead-zinc deposits and lead-zinc copper deposits is the economic quantities of copper bearing materials including chalcopyrite, covelite, chalcocite, bornite, enargite, digenite. Again, as in the case of the other ores, any pyrites and other iron sulfide minerals found in lead zinc ores are usually considered as gangue materials. However, they too may sometimes contain economic minerals substituted in the mineral's crystal lattice.
A similar process is commonly used for lead-zinc ore deposits and lead-zinc copper deposits (see generally FIGS. 10 and 11). Lead and zinc are separated by differential flotation. Obviously, the presence of high amounts of copper minerals would justify, from an economic standpoint, the production of a separate copper, lead, zinc concentrate. Such a process also begins with the introduction of a slurry of such ores (in a ground and or milled state) into a first stage, sparged-air-driven, differential froth flotation tank or system of such tanks in order to produce a low grade lead concentrate. Here again, collector reagents may be added at different stages during the process, e.g., in the grinding mill, to the ore pulp just prior to its introduction into the flotation cells, to the flotation cells or in several such places in the overall flow circuit. In the first stage of flotation, sphalerite pyrite and other gangue minerals are typically "depressed" through the use of cyanide and/or lime. Zinc depression is accomplished by the use of sodium sulfite or bi-sulfite in combination with zinc sulfate. The concentrate from the first stage is then collected and transported to a flotation tank or series of tanks, which also employ air sparging in order to separate and continue cleaning the lead concentrate. The tailings taken from the bottom of the differential flotation cell, which generally contain the majority of the zinc bearing mineral component to the ore, are then pumped to another series of sparged-air-driven tank or system of tanks. Several stages of cleaning may be required to produce the final zinc product. Copper sulfate is often added to activate the zinc minerals. The resulting thickened product containing the zinc concentrate produced by the overall flotation process is then sent (very often by slurry and pumping transport pipes) to a smelter. This final lead concentrate also very often contains minor economic gold, silver, and copper minerals. A copper-lead separation, when economically feasible, can be accomplished by another stage of differential flotation by depressing the lead and floating the copper or vice versa generally according to the flow scheme depicted in FIG. 12.
Thus it could be said that the correlative components of processing complex copper porphyry ores, copper magmatic ores, lead-zinc and copper-lead-zinc ores are based upon the following considerations. First of all, such ores of this type can be considered as complex ores whose major economic minerals are base metals including copper, lead, zinc, nickel, cobalt, and molybdenum. Such ores typically will require some degree of differential flotation as a means of processing and selective separation of one major economic mineral from another. Furthermore, most of these processes use multiple stages of sparged-air flotation tanks or series of such tanks. The differential flotation stage may be carried out at the beginning of the circuit, in the middle of the circuit or at the end of the circuit. Selective reagents (collectors activators, depressants and pH control agents) must be used to separate major economic minerals. Such collector reagents may be added at the different stages during the process. That is to say, they may be added at grinding mill, to the ore pulp just prior to its introduction into the flotation cells, to the flotation cells or at multiple places in the flow circuit. Moreover, regrinds of the ore may be carried out at several places in any given circuit. One or more stages of cleaning also are usually required of a major economic mineral in order to produce a final concentrate. It is also to be understood that all major ores may include minor economic minerals which usually include gold, silver, platinum or palladium group metals in varying amounts. And finally, those skilled in this art will also appreciate that selective actions against flotation of iron sulfides, including: pyrite, marcasite, arsenopyrite, pyrrhotite, magnetite and hematite may be necessary in processing many such ores.
On balance, the literature which serves to define this art will include the following references:
U.S. Pat. No. 1,022,085 teaches the use of a rougher cleaner circuit by the cleaning of rougher froth with cleaner cells with the cleaner tails returned to the rougher cells.
U.S. Pat. No. 1,020,353 teaches the use of sodium dichromate as a depressant for galena during differential flotation of complex ores.
U.S. Pat. No. 1,421,585 teaches a method for the treatment of complex ores by differential flotation through the use of cyanide and alkaline salts, such as sodium carbonate or sodium bicarbonate to depress shpalerite and pyrite during differential flotation of complex ores.
U.S. Pat. No. 1,469,042 teaches a process of differential flotation of complex ores to produce: (1) a lead mineral product free from zinc minerals; (2) a zinc mineral product free from lead, iron, and copper minerals; (3) a separation of copper minerals, iron minerals, precious metals with the lead mineral product rather than the zinc minerals; (4) a separation of the silver and gold minerals with the copper-iron-lead minerals product rather than the zinc mineral product; and (5) tailings product which no longer contains any valuable minerals. The process uses sodium sulfide, sodium monosulfide, or polysulfides of sodium to inhibit or depress zinc minerals while the other minerals are differentially removed.
U.S. Pat. No. 2,038,400 teaches the use of dithiophosphates as a flotation collector for copper which provides selectivity against pyrite.
3. Description Of Prior Art Re: Flotation Processes And Devices
It has long been appreciated that sparged air-driven, froth flotation is very effective for recovering ore particles having sizes between 300 and 20 um, but flotation efficiency commonly drops off as the particle size decreases below 20 um. This follows from the fact that whether or not a particle collides with a given bubble depends to a large degree on particle size and mass, bubble diameter, the balance of viscous, inertial, and gravitational forces acting on the particle and the form of the streamlines around the bubble.
Hence, one inability and/or inefficiency of sparged-air-driven tanks is its relative inability to separate gangue material from the economic minerals. That is to say that unwanted particles of gangue material becomes trapped (entrainment) between the immense volumes of large sparged-gas bubbles and are carried into the froth. Another inefficiency occurs during differential flotation stage when two major economic groups of minerals are sought to be separated using sparged-air-driven tanks. Here a greater portion of one major economic mineral or group of minerals is sought to be floated while the other major economic mineral or group of minerals is sought to be depressed. However, in sparged air-driven cells, particles of the economic minerals that are intended to be depressed are often trapped between the immense volumes of large sparged-gas bubbles and are carried into the froth.
For the most part, differential flotation processes have dealt with such inabilities and/or inefficiencies of sparged-air-driven flotation cells by "repeating" the same flotation in some of, or all of, the three general flotation stages previously discussed. That is to say that the relatively poor chances of a large bubble capturing a small particle have been dealt with by passing the ore pulp through successive flotation cells which comprise the first cell, the second and the third cell, i.e., the same basic sparged-air-driven froth flotation process is repeated over and over.
Similarly, the cleaning of gangue material from the froth concentrate is dealt with by passing froth concentrated recovery products through successive stages of cleaning. Each stage of cleaning can consist of a tank or a series of tanks through which the concentrate is passed. Each successive stage of cleaning removes a portion of the gangue material. In other words, the froth product is cleaned over and over until a desired grade is obtained.
Separation of economic minerals during the differential flotation stage is dealt with in a similar fashion, i.e., by passing the pulp through a series of sparged-air-driven tanks until a greater portion of one economic mineral is removed from a second economic mineral in order to deal with the problem of entrained particles from the second mineral remaining in the concentrate of the first. Thus, for example, the processing of copper porphyry ores by such prior art, sparged gas driven processes typically involve the use of: (1) a series of cells (rougher) which constitute a rougher, copper-molybdenite bearing froth; (2) a series of second cells (cleaners) for the purpose of cleaning the rough concentrated copper-molybdenite froth; (3) a series of third cells (differential flotation) to separate the copper and molybdenite; (4) a series of fourth cells (cleaners) to further "clean" the molybdenite. The processing of copper magmatic ores can use the same system as the copper porphyry ores, that is: (a) a series of first cells (rougher) which constitute a rougher, copper-cobalt or a copper-nickel bearing froth; (b) a series of second cells (cleaners) for the purpose of cleaning the rough concentrated copper-cobalt or copper-nickel froth; (c) a series of third cells (differential flotation) to separate the copper and cobalt or copper nickel; (d) a series of fourth cells (cleaners) used to clean the cobalt or nickel. However, the system also can be altered so that (1) a first series of cells (differential flotation) separates the copper from the cobalt or nickel; (2) a series of second cells (cleaners) which are used for the purpose of cleaning the rough concentrated copper froth; (3 and 4) a third and fourth series of cells (cleaners) used to clean the cobalt or nickel. In the case of lead-zinc deposits the system will preferably employ: (1) a first series of cells (differential flotation) which separates the lead from the zinc; (2) a series of second cells (cleaners) used for the purpose of cleaning the rough concentrated lead froth; (3 and 4) a third and fourth series of cells (cleaners) to clean the zinc. If copper is present in large enough quantities another stage of differential flotation may be added to separate the copper from the lead as well as to introduce additional stages of cleaning. It also is possible to have a system arranged in reverse order for lead-zinc recovery; that is, the zinc is differentially floated first followed by a cleaning of the lead.
Various processes have been used to produce a rising flow of gas bubbles for froth flotation of mineral and/or metal constituents of many kinds of ores. For example, as was previously noted, air has been sparged into froth flotation tanks in order to separate certain copper minerals from other metal bearing minerals as well as from the waste or gangue material with which they are usually associated. Copper bearing minerals which have been successfully recovered through the use of sparged-gas-driven flotation cells would include: chalcopyrite, covellite, chalcocite, bornite, bournonite, molybdenite, tentrahedrite-tennantite and polybasite. Such methods have also been widely used to recover certain mineral and/or metal constituents of various sulphide minerals such as arsenopyrite, pyrite, pyrrhotite, marcasite, enargite, galena, boulangerite, sphalerite, argentite, pentlandite, tentrahedrite-tennantite, pyrargyrite, stephanite, proustite, millerite, nickeline cobaltite, glaucodot, and skutterudite.
In one widely practiced flotation process, copper porphyry ores are concentrated by a process which begins with the introduction of such an ore (in a ground and/or milled state) into a first stage, sparged-air-driven, froth flotation tank or system of such tanks in order to produce a rough, copper-molybdenite bearing froth. A resulting rough concentrate obtained from the froth of the first cell is then upgraded in a second stage, or system of such second stage, sparged-air-driven, flotation tanks. The froth product of the second stage tank(s) is then collected and reduced to a bulk concentrate which is then transferred to a third, differential flotation tank, or series of such differential flotation tanks, which also employ air sparging in order to separate the bulk concentrate's copper constituents from its molybdenite constituents. In such a third, differential flotation cell systems, copper minerals are typically "depressed" through the use of sodium hydrosulfide. Moreover, burner oil is often used to "float" the molybdenite component of the ore. The tailings taken from the bottom of the differential flotation cell usually contain the majority of the copper bearing mineral component of the ore. Upon removal from the bottom of the differential flotation cell they are usually pumped to a final copper concentrate thickener. The resulting thickened product, containing the copper concentrate produced by the overall flotation process, is then sent (very often by slurrying and pumping transport pipes) to a smelter. Again, this final copper concentrate also very often contains precious metal components of the ore such as gold, silver, platinum and palladium as well as other metal constituents such as selenium and/or any of the molybdenum component which was not recovered by the reverse flotation process.
The gas bubbles used in each of the above noted, prior art, sparged gas-driven first, second and third stage flotation cells are typically employed in concentrations of from about 25 to about 70 bubbles per cubic centimeter of the fluid media. Such sparged-gas-produced bubbles normally will have average bubble diameters of from about 0.2 to about 1.4 millimeters (mm). There are, however, some drawbacks to the use of such sparged-gas-driven flotation systems. For example, it has been found that sparged-gas-produced bubbles of such sizes are not particularly effective in associating themselves with certain smaller mineral particles (e.g., those having average diameters of 0.020 mm or less), especially when they are introduced into the first cell(s) of the differential flotation process previously noted.
Consequently, flotation cell systems employing smaller bubbles, and especially those relatively smaller bubbles generated by electrolytic decomposition of water, have been suggested and/or employed as alternatives and/or supplements to various kinds of sparged-gas-driven flotation cells. For example, bubbles produced by electrylic decomposition of water (e.g., hydrogen and/or oxygen) have been employed to recover certain metal and/or ore constituents from certain metal-containing sources. However, those sources wherein electrolytically produced bubbles have been successfully employed are in the general nature of relatively small quantities of toxic products produced by various industrial processes.
For example, some specific examples of electrolysis-bubble-driven flotation cell systems which have been used in various branches of the prior art would include:
(1) Articles by (a) E. H. Crabtree and J. D. Vincent entitled: Historical Outline of Major Flotation Developments and (b) by Pierre R. Hines and J. D. Vincent entitled: The Early Days Froth Flotation, 50th Anniversary Volume, Society of Mining Engineers, D. W. Fuerstenau, Editor.
(2) An article by Glembotsky et. al., entitled Selective Separation of Fine Mineral Slimes Using The Method of Electric Flotation, is found in a publication entitled Electrochemistry in Industrial Processing & Biology. It teaches use of electrolytically generated hydrogen, oxygen (and/or air bubbles) to float fine mineral particles such as those of manganese. With respect to electrolytic-bubble-driven flotation in general, this article notes a general agreement on the effectiveness of the following process parameters: a 0.5 to 1.0 meter height of the cell's liquid column, a current density of from 0.01 to 0.03 A/cm.sup.2 and an electric power consumption of from about 0.5 to about 2.0 KWh/m.sup.3.
The Glembotsky reference also implies the use of electroflotation for processing gold and silver in systems wherein these precious metals are the major economic minerals. They are specifically recovered by use of xanthate flotation agents. Those skilled in this art will appreciate that ore deposits containing gold or silver as major economic minerals also often contain chalcopyrite as a minor economic mineral and that a bulk sulfide flotation process is almost exclusively used for treatment of these ores, since selective separation of these minerals can be most economically done at a smelter. Concentrates containing say 10 ounces of gold, 10 ounces of silver, as the major economic minerals and 5% copper or lead as the minor economic minerals are quite profitable to ship to a smelter. Again, xanthate is used as a collector for these ores since economic gold values are often found in ariforus pyrite, marcasite, arsenopyrite, pyrrhotite, and chalcopyrite. However, a bulk sulfide flotation process such as that taught by Glembotsky is an unacceptable process for recovering base metal deposits such as copper porphyries, magmatic copper, lead-zinc and copper-lead-zinc deposits because these concentrates must contain a minimum of 30% and often better than 50% copper, lead, zinc, or nickel in order to economically justify shipment to a smelter. Furthermore, molybdenite must be cleaned to purities in excess of 90%. Consequently, xanthate is not typically used in their differential flotation because of its selective action against pyrite which is often a gangue mineral in copper, lead, and zinc ores. Nor is xanthate selective for certain specific economic minerals. Moreover, the cyanide and lime typically used in differential flotation of copper, lead, zinc ores would never be used with a gold-silver ore since the economic minerals would be depressed.
However, none of these references are particularly concerned with an efficient process of flotation of copper porphyry ores, copper magmatic ores, lead zinc ores, and copper lead zinc ores through the use of electroflotation systems used in conjunction with sparged gas driven flotation systems. Moreover, none of the above noted methods and/or apparatus were intended to be retrofitted into existing flotation cells. Moreover, none of the above methods would be as effective in collecting the wide range of particle sizes or as efficient in separating economic minerals during differential flotation.
(3) U.S. Pat. No. 4,101,409 teaches use of electrolytically generated gas bubbles to attract suspended solids. The process is specifically aided by introducing air into the tank to increase the gas available for flotation purposes.
(4) U.S. Pat. No. 4,623,436 teaches a method of removing impurities from a liquid by carrying out electrolysis at a pressure higher than atmospheric. The liquid is then exposed to atmospheric pressure and, hence, a decompression. Fine bubbles resulting from the decompression attach to impurities in the liquid.
(5) U.S. Pat. No. 3,552,571 teaches a "generalized" (no particular liquid such as water is emphasized) electroflotation device having certain hardware and geometrical details. For example, the device has a grate of electrodes positioned horizontally across the tank to produce a rising flow of gas bubbles produced by the electrolysis. The electrolysis action is supplemented by a distributor arm which rotates to evenly distribute the liquid which is to be electrolytically broken down.
(6) U.S. Pat. No. 3,726,780 discloses an electroflotation apparatus chiefly characterized by employment of having a tank whose height is several times its diameter and wherein a plurality of horizontal electrodes is disposed throughout the height of the tank. Typical liquids broken down in the tank by the electrolysis action may be milk water waste, oily waste water and dye plant waste.
(7) U.S. Pat. No. 3,853,736 teaches concepts very similar to those of U.S. Pat. No. 3,726,780 in that both systems utilize tanks having heights several times their effective diameters and a plurality of horizontal electrodes disposed throughout the respective tanks. Conduits and controls are provided to induce a downflow of liquid to be purified. Here again such a liquid might include oily waste water.
(8) U.S. Pat. No. 3,888,751 teaches a method of purifying waste water by the formation of oxygen and hydrogen bubbles from the electrolysis of water and directing a flow of said waste water into the bubbles in order to promote nuclei formation which aids in coagulation of the waste material around the nuclei. The formation of negative colloids of sulfides of various metals including those of gold and silver are noted.
(9) U.S. Pat. No. 3,898,150 teaches a electroflotation apparatus having grid structures having units wherein a plurality of parallel electrodes attached to a bus bar and embedded in a nonconducting support.
(10) U.S. Pat. No. 3,944,478 teaches electrolytic treatment of drainage in conjunction with a flocculation process; the process is carried out with aluminum ions or iron ions eluted by electrolysis.
(11) U.S. Pat. No. 3,970,536 teaches a method of treating an oil and particulate containing liquid coolant by flowing said coolant into a tank having several, alternating, oppositely charged plates. Under such conditions, the contaminates tend to agglomerate. Upwardly flowing gas bubbles generated by the plates entrain the agglomerated contaminates which are then skimmed from surface of the liquid.
(12) U.S. Pat. No. 3,975,269 discloses a method of purifying waste water by use of microbubbles of oxygen, hydrogen (or air) which attract contaminants in the waste water by differences in electrostatic charge in order to form embryo flocs which are buoyed to the surface. A polyelectrolyte is also added to aid in the formation of a full floc which is then collected.
(13) U.S. Pat. No. 3,989,608 teaches removal of hexavalent chromium (or other metal-ion contaminates) from cooling tower blowdown water. Its most novel feature is that the electrochemical operation is conducted under an evolved-hydrogen partial pressure greater than atmospheric pressure.
(14) U.S. Pat. No. 4,120,765 teaches confining electrolytically generated bubbles in a columnar treating region in order to get full use of the rising bubbles. Regulation of the bubble outlet relative to the liquid's surface can also be used to regulate the character of the foam produced by the bubbles.
(15) U.S. Pat. No. 4,202,767 teaches a method for purifying waste water by an electroflotation system wherein one of the electrodes is positioned horizontally above the other electrode. The electrodes themselves are formed of a perforated material.
(16) U.S. Pat. No. 4,224,148 teaches introduction of a galvanically charged particulate despension into a waste water stream and running the resulting mixture into treatment zones. The patent observes that gaseous oxygen adheres to certain particle surfaces. Oxidation is further promoted by pH adjustment with sulfur dioxide. The medium is then neutralized, brought to a pH of 10-11 and the contaminant is then precipitated with the aid of a galvanic grounding of said medium. Among other things precious metals may be recovered by this method.
All of the above noted processes may also be contrasted to mining operations wherein the cost of producing bubbles by electrolytic decomposition of water in the general context of refining large quantities of bulk ores has been heretofore regarded as prohibitive. This is especially true in the case of electrolytic flotation of copper porphyry, copper magmatic ores, lead-zinc ores, lead-zinc-copper ores. For example the cost of producing a pound of final copper concentrate (i.e., the concentrate product of the "third", differential flotation cell noted above), solely by means of electrolytically generated bubbles generated in first, second and third cells (analogous to the first, second and third, sparged-air-driven, cells noted above) would be several times the cost of using sparged air-driven systems.